In recent days, resin materials have been widely employed in various fields, and for the purpose of satisfying physical and chemical properties required for the resin materials, there have been developed various resin compositions by incorporating additives, fillers, reinforcing agents, etc. to various resins.
For example, in accordance with the integration of electronic components, physical and chemical properties (specifically, heat resistance and flame retardance) of extremely high level have been required for the resin materials used in this electronic art. The resin materials are utilized as prinitable circuit boards, semiconductor packages, etc. of electric or electronic parts. As is well known, the electric or electronic components work upon application of an electric current, and in this stage a heat is generated. As the electronic machines have been used in more various surroundings or the electric circuits have been made more integrated recently, the printable circuit boards or the semiconductor packages are used continuously and at extremely high temperatures, and hence heat resistance and flame retardance of much higher level are eagerly required for the resin materials used therefor.
As an organic material having high heat resistance and high flame retardance, a flame-retardant resin composition obtained by adding a halogenated organic compound and an antimony-containing compound to a thermoplastic resin is employed.
Among thermoplastic resins, polyamides are known as engineering plastics being excellent in mechanical and chemical properties, and a representative example of polyamides is nylon. In the practical use, various additives can be added to the polyamides depending on the purpose. Most of the polyamide resins have a melting point higher than that of other resins such as polyphenyl sulfide. Further, these polyamide resins have a high crystallinity, and they are excellent in other properties such as heat distortion resistance of the resin without reinforcement, sliding properties and fatigue resistance.
Among the polyamide resins, aliphatic polyamides represented by nylon 6 and nylon 66 are utilized in the art of synthetic fibers. It is known that a copper-containing compound is added to the aliphatic polyamides to obtain compositions which are hardly oxidized even when exposed to high temperatures for a long period of time to be inhibited from the lowering of the mechanical properties.
Further, it has been recently known that the aromatic polyamides are excellent in various properties such as abrasion resistance, strength, chemical resistance, heat resistance and molding properties. Therefore, the aromatic polyamides are utilized as engineering plastics employable as resin materials for automobile industry and for electrical industry.
However, those conventional resin compositions still have various problems.
For example, the above-mentioned flame-retardant resin composition comprising a thermoplastic resin, a halogenated organic compound and an antimony-containing compound often brings about strand-foaming in the granulation stage or coloring of pellets.
Further, when the flame-retardant polyamide resin, that is one of the thermoplastic resins, is subjected to continuous injection molding for a long period of time, a mold of the molding machine might be little by little deposited with a decomposition product of the resin (this deposition is referred to hereinafter as "mold-staining"). If the mold-staining occurs, the transfer efficiency of the mold tends to lower or the decomposition product of the resin is easily introduced into the resulting molded product. Moreover, a gas bent is choked up with the decomposition product of the resin to cause burn marks of the resin.
For these reasons, the mold is generally cleaned at regular intervals to remove stains from the mold. For cleaning the mold, the molding operation is compelled to be stopped, and as a result, the production of the molded products is stopped.
From the viewpoint of productivity, therefore, eagerly desired are flame-retardant polyamide resins which hardly bring about mold-staining.
In the art of electronic parts, there has been recently employed a method comprising fitting electronic components having a part formed from the polyamide resin (such as housing thereof) onto a printable wiring board and then firmly fixing the electronic components to the board utilizing infrared rays reflow-soldering. However, the conventional polyamide resin compositions are unsuitable for this method, because they are insufficient in the heat resistance and the flame retardance.
The infrared rays reflow-soldering is a method for fixing electronic components onto the circuit board. The method comprises temporarily fixing the electronic components onto the predetermined portions of a circuit board which has been beforehand provided with solder dots on the portions, and melting the solder under irradiation of the board with infrared rays to firmly fix the electronic components onto the circuit.
In the conventional method for fixing the electronic components onto the circuit board using a solder bath, it is difficult to fit the electronic components on the board with a high denseness, so that the above-mentioned infrared rays reflow-soldering has been employed instead of the conventional method, to improve the denseness.
However, a problem still resides in the infrared rays reflow-soldering. That is, infrared rays are applied from the upper side of the board in this method, and the electronic part-forming materials using conventional polyamide resin compositions have a low melting point as well as ABS resin, polycarbonate and polybutylene terephthalate, so that the temperature for the infrared rays reflow-soldering cannot be sufficiently raised.
Japanese Patent Provisional Publication No. 36(1961)-317552 discloses nylon 46 containing a brominated crosslinking aromatic polymer as the flame-retardant resin composition formed by using brominated compounds of polyvinyl aromatic compounds (e.g., divinylbenzene and divinylxylene) or brominated compounds of crosslinking aromatic polymers synthesized by forming a crosslinking structure in linear polyvinyl compounds such as polystyrene, polyvinyltoluene, polymethylstyrene and polyvinyltoluene in addition to monovinyl aromatic compounds (e.g., styrene, methylstyrene and vinyltoluene) are employed in the publication.
The above publication describes that the flame-retardants are effectively employed for nylon 46, but does not describe any relationship between the flame-retardants and other polyamides.
The present inventors have found that the aromatic polyamides are excellent in mechanical properties and in heat resistance of a short term, but they markedly deteriorate in the mechanical properties because of oxidation thereof when exposed to high temperatures for a long period of time. For improving the mechanical properties of the aromatic polyamides, a method of adding copper-containing compounds to the aromatic polyamides can be thought as in the aforementioned aliphatic polyamides. However, if the copper-containing compounds are added to the aromatic polyamides, any satisfactory effects cannot be obtained.
The present inventors have earnestly studied to solve the above-described problems existing in the prior arts, and as a result, they obtained the following findings and accomplished the invention.
That is, the resin compositions comprising a thermoplastic resin, a halogenated organic compound and an antimony-containing compound can be remarkably improved in granulation properties and color shades of pellets, by adding a phosphorus-containing compound thereto. In addition, other properties of the compositions such as heat resistance and flame retardance are never marred even by adding the phosphorus-containing compound.
Moreover, thus obtained resin compositions (i.e., flame-retardant resins) can reduce occurrence of the aforementioned mold-staining by adding thereto at least one of an amine-type stabilizer and a phosphorus-type stabilizer.
In the case of using polyamide as the thermoplastic resin, if a brominated compound of a polymer formed from an aromatic vinyl compound and a specific carboxylic acid is introduced into a resin composition, the resulting resin composition can be provided with an extremely high flame retardance.
Further, if an aromatic amine-type stabilizer and an organic phosphite-type stabilizer are added to a specific aromatic polyamide, there can be obtained a resin composition having high heat aging characteristics and showing high heat stability in the molding stage.